The present invention relates to a two-stage operation push-on switch wherein a first switch operates with a pressing force applied thereto and then a second switch operates with click feeling.
A push-on switch used in the input unit of recently available electronic equipment extremely reduced in size and increased in density is required to be compact and narrow width because the mounting space of the switch is limited.
A conventional push-on switch is described with reference to FIG. 26 to FIG. 31.
FIG. 26 is an appearance perspective view of a conventional push-on switch. FIG. 27 is a front sectional view of the switch.
FIG. 28 is a plan view of a switch case that is an essential portion of the switch. FIG. 29 is a plan view of a movable contact that is an essential portion of the switch.
Switch case 1 made of insulating resin is provided with a circular recess 1A at the top thereof. On the inner bottom of the recess 1A are disposed a central fixed contact 2A, and two peripheral fixed contacts 2B, 2C being electrically independent and positioned in point-to-point symmetric relation to each other with the central fixed contact therebetween. At the periphery of the case 1 are arranged connecting terminals 3A to 3C conducting with each fixed contact 2A to 2C.
Movable contact 4 made of elastic sheet metal is formed of a dome portion 5 curved upward and a circular ring portion 7. The diameter of the dome portion 5 is nearly equal to the distance between the centers of the fixed contacts 2B, 2C. The dome portion 5 and the ring portion 7 are connected to each other by a flexible thin connection 6 in such manner that the dome portion 5 is maintained in a state of being sloped against the ring portion 7.
The movable contact 4 is housed in the circular recess 1A of the switch case 1 in such manner that the periphery of the dome portion 5 is positioned at spaced intervals above the peripheral fixed contacts 2B, 2C.
Sheet 8 made of elastic insulating film covers the upper opening of the switch case 1. The sheet 8 is held on the top of the switch case 1 by means of a cover 9 having a through-hole 9A at the center thereof.
The operation of a conventional push-on switch having such a configuration will be described by using the front sectional views of FIG. 30 and FIG. 31.
First, the operation of the first switch is described with reference to FIG. 30. When the dome portion 5 of the movable contact 4 is pressed by operating means 10 (shown by chain double-dashed line) from the through-hole 9A of the cover 9 via the sheet 8, then the connection 6 is flexed. At the time, the dome portion 5 is still in a spherical shape. And, the dome portion 5 moves downward and its periphery comes into contact with the peripheral fixed contacts 2B and 2C. That is, the connecting terminals 3B and 3C become conductive.
Next, the operation of the second switch is described with reference to FIG. 31. After causing the terminals 3B, 3C to become conductive, when the dome portion 5 of the movable contact 4 is further strongly pressed by the operating means 10, the dome portion 5 is elastically reversed downward with click feeling. Then the central of the dome portion 5 comes into contact with the central fixed contact 2A, causing the terminals 3A, 3B and 3C to become conductive.
After that, when the pressing force given by the operating means 10 to the dome portion 5 is released, the dome portion 5 is elastically restored with click feeling upward to the original spherical shape. And, the center of the dome portion 5 moves off from the central fixed contact 2A, causing the second switch to be turned off. Subsequently, as the connection 6 returns to the original state of being sloped upward, the periphery of the dome portion 5 shown in FIG. 27 moves off from the peripheral fixed contacts 2B, 2C, and the first switch is also turned off.
As a prior art document related to the present invention, Japanese Laid-open Patent H11-232962 is well known.
As described above, in the conventional push-on switch, since the circular ring portion 7 is concentrically arranged outside the dome portion 5, the outside shape of the switch case 1 or the outside shape of the push-on switch is to be enlarged. As a result, a large mounting space will be required.
Also, with diversification of recent equipment, two-stage push-on switches as described above are required to be capable of being operated by various operating forces. However, in the case of the conventional switch, the first switch and the second switch are operated by the movable contact 4 with the dome portion 5 and the circular ring portion 7 integrated therein. Accordingly, it is difficult to change the setting of the operating force for each switch.
The present invention is intended to solve such conventional problem, and the purpose is to provide a two-stage push-on switch being narrow and less in mounting space, wherein it is easy to set the operating force for each switch.
In order to achieve the above purpose, the push-on switch of the present invention comprises:
1) a switch case made of insulating resin opening upward;
2) a central fixed contact disposed on the inner bottom of the switch case;
3) two peripheral fixed contacts disposed with the central fixed contact therebetween on the inner bottom of the switch case;
4) connecting terminals individually electrically connected to the central fixed contact and the two peripheral fixed contacts at the periphery of the switch case;
5) a first movable contact made of elastic sheet metal provided with a hole at the center thereof, wherein the first movable contact includes a ring portion, and a projection extended to the right and left of the ring portion, and the first movable contact is disposed in the switch case in such manner that the ring portion is arranged above the two peripheral fixed contacts in confronting spaced relation thereto;
6) a second movable contact having a dome portion curved upward in spherical shape, which is disposed on the ring portion of the first movable contact; and
7) a driving means having a pressing portion for pressing the dome portion of the second movable contact, which is arranged and vertically movable above the second movable contact.